A detailed discussion of background information is set forth in U.S. patent application Ser. Nos. 14/069,760 and 13/686,862 which is incorporated by reference herein.
Electronic crash sensors used to sense crashes for airbag deployment currently in production comprise one or more MEMS accelerometers that measure acceleration at the sensor location. These accelerometers are typically produced by micromachining a single crystal of silicon and the sensing elements are frequently in the form of a beam or tuning fork. The silicon crystal typically has residual stresses that can cause the mechanical structure of the accelerometer to change geometrically as a function of time and/or temperature unpredictably. As a result, properties of the accelerometer similarly can change with time and temperature. To overcome this inherent problem, additional apparatus is designed into the accelerometer to permit the acceleration sensing beam or tuning fork to be excited and its response tested. These accelerometers are continuously self-tested and adjusted as their properties change to maintain proper calibration. This adds cost and complexity to the accelerometer and sensor software design. This self-testing feature also increasingly complicates the device design if more than one axis is simultaneously tested.
Accelerometers are also used in vehicle navigation systems such as on some state snow plows for accurately locating the vehicle on a snow covered roadway. However, rather than calibrating each inertial device by using GPS, they are inherently accurate devices which are calibrated in a laboratory. They are used to interpolate vehicle positions between GPS readings. Such devices are not used to determine the angular position of cameras.
All of the patents, patent applications, technical papers and other references mentioned herein and in the related applications are incorporated by reference herein in their entirety. No admission is made that any or all of these references are prior art and indeed, it is contemplated that they may not be available as prior art.
Definitions of terms used in the specification and claims are also found in the above-mentioned applications.